Effect of Decreasing Peripheral Skin Blood Flow Via Local Axon Reflexes, Decreases in Perfusion Pressure, and Ischemia during Systemic Thermal-Induced Eccrine Sweating in Humans

In humans, skin blood flow (SkBF) and sweating are tightly coupled, suggesting common neural control and regulation. This study was designed to separate these two sympathetic nervous system end-organ responses via SkBF-decreasing mechanical perturbations in the presence of a strong sudomotor drive. Two women and 4 men (age 26±1 yrs and BMI 24±4 kg/m2) were tested in normothermia and heat stress conditions by pumping neutral (34°C) and hot (46-50°C) water through a high-density tube-lined suit to either maintain internal temperature (pill telemetry) or increase it by ~1.0°C. Arm and leg SkBF (laser-Doppler flowmetry) was decreased by engaging the venoarteriolar response (limb lowered ~30 cm from heart level; CVAR), venoarteriolar response plus a decrease in perfusion pressure (venous occlusion by proximal cuff inflation; CVAR with DPP), and ischemia (arterial occlusion by proximal cuff inflation). Decreased SkBF was observed with CVAR (30±7 and 60±15%), CVAR with DPP (44±12 and 86±11%), and ischemia (96±1 and 99±1% for the arm and leg, respectively) during normothermia. Despite these significant decreases in SkBF, there were no significant effects on transepidermal water loss (TEWL). Heat stress increased intestinal temperature from 37.1±0.1 to 38.0±0.1°C, heart rate (ECG) from 65±5 to 93±4 bpm, arm cutaneous vascular conductance (SkBF/Mean arterial pressure*100) 52±12 to 473±85 units, and forearm sweat rate (capacitance hygrometry) from 0.0 to 0.6±0.1 mg/ml/min. During heat stress, decreased SkBF was also observed during CVAR (20±7 and 17±6%), CVAR with DPP (39±9 and 52±13%), and ischemia (99±1 and 100±1% for the arm and leg, respectively). Despite these significant decreases in SkBF, eccrine sweat rate was not significantly affected. These data indicate that a wide range of acute changes in SkBF do not appear to affect TEWL or eccrine sweating in peripheral skin, indicating that there is independent neural control and regulation of these two sympathetically controlled end-organs